This invention relates to an extruder and more particularly to a method and apparatus for co-extruding a thin formed thermoplastic sheet.
In the production of a co-extruded article, it was found desirable to laminate plastic film of diverse properties such as low density, high melt index to another material having high density but low melt index. This type of co-extrusion although found more desirable than lamination after separate extrusions had difficulty in bringing the separate melts from different extruders into a common manifold for joining because the equipment was relatively expensive and complex. The present invention overcomes these objections by introducing a separate extruder block which is disposed adjacent the fully formed article prior to the die opening to facilitate the lateral expansion of the second melt onto the lateral expanded first melt. This apparatus and method facilitates its introduction into a system and is particularly effective in applying a cap stock such as the second melt as a thin film over a controlled portion only of the expanded primary melt. Such apparatus facilitates the quick removal of a separate feedblock and returning the extruder to its former single fold function of being a conventional extruder.